<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
</head>

<body>
  <script>
    // <p class="demo">hello JavaScript</p> 内部的文按

    function testReg() {
      var reg = /^<.+>.+<.+>$/;
      var str = '<p class="demo">hello JavaScript</p>'.replace(/^<.+>(.+)<.+>$/, function (match, $1) {
        return $1;
      })
      console.log(str);
    }

    testReg();





  </script>
</body>

</html>